Flexible polyurethane foams are widely used in numerous applications. Main sectors of application are automotive and aircraft industry, upholstered furniture and technical articles. For instance, full foam seats, top pads for the seats and restraints for back and head, all made from flexible polyurethane foam, are widely used in cars and aeroplanes. Other applications include the use of flexible polyurethane foam as carpet backings, foamed seat saddles for motorbikes, gaskets between a car body and its lights, lip seals of air filters for engines and insulating layer on car parts and engine parts to reduce sound and vibration. It will be appreciated that each specific application puts its own demands on the flexible foam to be used. Important characteristics in this connection are density, hardness, resilience and dampening behaviour of the foam and in order to fit each application, these characteristics should be optimally balanced and adjusted. The present invention aims to provide a polyol formulation suitable for producing flexible polyurethane foams having a latex-like stress/strain behaviour, i.e. a soft initial touch followed by a rapidly increasing support upon further compression of the foam combined with excellent resilience and foam hardness properties.
In International patent specification No. WO 95/09886 latex-like polyurethane foams are disclosed, which are obtained by reacting three different polyols, an isocyanate having a functionality of from 2.0 to 2.7 and an isocyanate index of 75 to 100, water and an auxiliary blowing agent and an amine catalyst. The polyols used are (i) a major amount of a triol polyol having a primary hydroxyl content of 50-80%, an ethylene oxide content of 10-25% and a molecular weight of 3,000-6,500; (ii) a minor amount of a polymer triol polyol having a molecular weight of 3,000-6,500 and (iii) a very minor amount of a triol polyol having a primary hydroxyl content of 50-90% and an ethylene oxide content of 40-90%. It would be advantageous from a cost perspective, if the number of polyols could be reduced, while still obtaining a flexible polyurethane foam exhibiting a latex-like appearance and behaviour. Furthermore, the option of using water as the sole blowing agent, whilst still being able to obtain a latex-like polyurethane foam, would be desirable from an environmental point of view and for reasons of process efficiency and economy. The present invention, accordingly, aims to reduce the number of polyols to be used and to offer the possibility of using water as the sole blowing agent, whilst still obtaining a latex-like polyurethane foam.
In U.S. Pat. No. 5,011,908 a polymer polyol composition for producing flexible polyurethane foams is disclosed, which composition comprises a major amount of high functionality polyol, a minor amount of a subsidiary polyalkylene oxide polyol and a stably dispersed polymer. The high functionality polyol suitably has an average nominal functionality of at least 3, an ethylene oxide content of between 8 and 25% and an equivalent weight of between 1,000 and 3,000. From the disclosure it is apparent that this high functionality polyol advantageously is a formulation of at least two different polyalkylene oxide polyols, as is most evidently demonstrated by the working examples. The subsidiary polyalkylene oxide polyol suitably has an average nominal functionality up to 8, an ethylene oxide content of between 30 and 100% and a molecular weight of between 450 and 30,000 with a clear preference for the lower molecular weight (450 to 2000) liquids. The formulation of both polyol components should have an average nominal functionality of at least 3.0. The polymer, finally, is present in an amount of from 2 to 50% by weight based on total weight of the polymer polyol components and can be any standard vinyl polymer or copolymer, a polyurea-type polymer or a condensation product of a polyfunctional glycol or glycol amine and a diisocyanate. Styrene-acrylonitrile polymers and styrene-acrylonitrile-vinylidene polymers are presented as the preferred polymers.
Although the flexible polyurethane foams produced from the polymer polyol composition disclosed in U.S. Pat. No. 5,011,908 exhibit a good resilience, the formulation used is relatively complicated, thus leaving a need for a more simple formulation. Furthermore, one of the objectives of this U.S. patent is to provide polymer polyol compositions for producing high resilience flexible polyurethane foams having densities below 1.8 pounds per cubic foot (i.e. below 28.8 kg/m.sup.3), as is also clearly illustrated by the working examples. Finally, U.S. Pat. No. 5,011,908 is silent about any latex-like appearance or behaviour of the flexible foams disclosed. The present invention aims to provide a simplified polyol formulation, which enables the production of flexible polyurethane foams exhibiting an excellent resilience, even at higher densities (i.e. above 28.8 kg/m.sup.3), while at the same time exhibiting the latex-like behaviour mentioned hereinbefore. More generally, the present invention aims to provide a polyol formulation from which flexible polyurethane foams can be prepared having a latex-like stress/strain behaviour, thus making these foams very suitable as cushioning material which can be used in numerous applications like the full foam seats, top pads for seats and restraints for back and head referred to above.